fix: glyph overflow in text layout, affecting text_size and draw_text_mut

[var4yn]

ISSUE: #710

Problem

When rendering glyphs that extend beyond the font's ascent line (e.g. Ä, Ö, Ü),
the returned text_size did not account for the overshoot, causing the rendered text
to be clipped.

Solution

Added an second cycle in layout_glyphs to compute above_ascent and below_ascent
values.

• above_y: the minimum value among glyphs that extend above the ascent line (less than zero).
• below_y: the minimum value among glyphs that extend below the ascent line (greater than zero).

These values are used to calculate the correct height and correct offset_y in layout_glyphs.

Before / After

Upd: The font from the issue is used. The changes are clearly visible.

Before	After

[var4yn]

For old tests - test_draw_text, test_draw_text_with_alpha, truth images need to be replaced.

I'm ready to do this if this PR is of interest

[var4yn]

I just noticed that the fix isn't very visible on the DejaVu font.
Perhaps I should update the font in the tests to the font from the example in the issue.

[var4yn]

Code to generate Before/After images:

use image::RgbaImage;

macro_rules! txt_img {
    ($func_name:ident, $imageproc: ident) => {
        pub fn $func_name(word: &str) -> RgbaImage {
            let mplantin = include_bytes!("../fonts/mplantin.ttf");
            let mplantin = ab_glyph::FontArc::try_from_slice(mplantin).unwrap();

            let font_size = 128.0;

            let (w, h) = $imageproc::drawing::text_size(font_size, &mplantin, word);
            let mut image = RgbaImage::from_pixel(w, h, image::Rgba([0, 0, 0, 255]));

            $imageproc::drawing::draw_text_mut(
                &mut image,
                image::Rgba([100u8, 100u8, 100u8, 255u8]),
                0,
                0,
                font_size,
                &mplantin,
                word,
            );

            image
        }
    };
}

txt_img!(txt_img_before_fix, imageproc);
txt_img!(txt_img_after_fix,  imageproc_2);

fn main() {
    
    let words = [
        ("ÁÄaaa", "out"),
        ("Á", "symbol2"),
        ("Äabcpghky", "symbols"),
        ("abcpghky", "symbols_little"),
        ("1.", "number"),
    ];

    for (word, filename) in words {

        let img_before = txt_img_before_fix(word);
        let img_after = txt_img_after_fix(word);

        img_before.save(format!("{}.png", filename)).ok();
        img_after.save(format!("{}_after_fix.png", filename)).ok();

    }
}